1. Field of the Invention
The invention relates to a regulator valve provided in a hydraulic control apparatus of an automatic transmission. More particularly, the invention relates to a regulator valve suitable for use as a primary regulator valve that controls line pressure.
2. Description of the Related Art
A hydraulic control apparatus that controls a vehicular automatic transmission is provided with a plurality of valves in a valve body mounted to a shift mechanism. This hydraulic control apparatus controls a plurality of friction apply elements in the transmission by regulating the hydraulic pressure and switching the supply and discharge path of hydraulic fluid discharged from an oil pump, using these valves. One of the valves provided is a regulator valve which controls the line pressure which is the base for the apply pressure of the individual friction apply elements in the automatic transmission. This regulator valve is provided to regulate the pressure of the hydraulic fluid discharged from the oil pump according to the vehicle speed, the throttle opening amount, and the like.
Typically in this regulator valve, a valve spool that appropriately connects a supply pressure port to which line pressure is supplied with a drain port is urged to one side in the axial direction by line pressure to be regulated being applied from one end, and is urged to the other side in the axial direction by urging force corresponding to a coil spring which is interposed between the valve body and the valve spool at the other end, and throttle pressure that is generated according to engine output.
Japanese Patent No. 3087326, Japanese Patent Application Publication No. 2006-153238 (JP-A-2006-153238), and Japanese Patent Application Publication No. 5-99302 (JP-A-5-99302), for example, describe regulator valves that regulate the line pressure PL in the following manner. FIG. 3 shows a specific example of this type of regulator valve. As shown in FIG. 3, a coil spring 32 and a spring receiving sleeve 34 are provided inside a valve chamber 33 of a valve body 31. This spring receiving sleeve 34 axially displaceably houses a straight plunger 36, one end of which faces a valve spool 35 and the other end of which receives reverse range pressure PL(R). As a result, both throttle pressure PSLT and operating force corresponding to the reverse range pressure PL(R) from the straight plunger 36 are applied to the valve spool 35 when the reverse range is selected.
In addition, Japanese Patent Application Publication No. 5-157174 (JP-A-5-157174), for example, describes another such regulator valve, an example of which is shown in FIG. 4. With this kind of regulator valve, a stepped plunger 46 having two lands 46a and 46b with different diameters is housed inside a spring receiving portion 44. The large diameter land 46a is provided on the side of the stepped plunger 46 that is closest to a spool 45. Reverse range pressure PL(R) is applied between these two lands 46a and 46b, while throttle pressure PSLT is applied to the back side of the small diameter land 46b. 
Incidentally, reference characters A1 and A2 in FIG. 3 and reference character A1 in FIG. 4 denote the land portion pressure receiving areas of both ends of each of the valve spools 35 and 45, respectively. Similarly, reference character A3 in FIG. 3 and reference characters A3 and A4 in FIG. 4 denote the land portion pressure receiving areas of both ends of each of the plungers 36 and 46, respectively.
Also, Japanese Patent Application Publication No. 9-79361 (JP-A-9-79361), for example, describes another regulator valve in which throttle pressure is applied between large and small lands of a stepped plunger, while throttle pressure, not reverse range pressure PL(R) is also applied to the back side of the large diameter land, which is the side of the land farthest from a valve spool for regulating the line pressure.
However, with the regulator valve of the related art such as that described above, force which acts on the valve spools 35 and 45 but which does not appear in a pressure regulating expression, such as flow force or the like, may cause the line pressure to increase beyond the pressure for which the regulator valve was designed (i.e., beyond the designed value). That is, a so-called rising amount may increase.
One effective measure to prevent this is to increase the feedback effective pressure receiving area (which corresponds to A1-A3 for the straight plunger 36 and A1-(A3-A4) for the stepped plunger 46, for example). However, if the pressure receiving area A3 of the plungers 36 and 46 of the related art is reduced, the gain of the throttle pressure PSLT will also simultaneously decrease. As a result, the necessary conditions for regulating the line pressure will no longer be satisfied.
That is, with a straight plunger such as the plunger 36, if the pressure receiving area A3 of the plunger 36 is reduced, the valve gain of the throttle pressure PSLT will decrease, and as a result, the necessary line pressure when the throttle is fully open will not be able to be achieved.
Also, with the stepped plunger of the related art, the plunger moves even in the drive range so the only way to increase the feedback effective pressure receiving area without changing the pressure receiving area A3 which affects the drive range pressure setting is to increase the pressure receiving area A4. As a result, however, the gain of the throttle pressure decreases such that the necessary line pressure when the throttle is fully open is unable to be achieved. Furthermore, because the plunger 46 moves even in the drive range, the stability of the hydraulic control may decline. In addition, the plunger 46 is not easy to be assembled.
Moreover, with both of the regulator valves of the related art, the decrease in the gain of the throttle pressure can be compensated for by increasing the throttle pressure receiving area on the valve spool 35 and 45 side. Doing this, however, would increase the size of the valve, which means that the valve would require more mounting space.
For these reasons, it is difficult for the regulator valves of the related art to ensure both feedback effective pressure receiving area and the necessary line pressure, while fitting into a limited space.